Flow rate sensor

ABSTRACT

In a flow rate sensor, a sensing passage, into which a fluid is introduced and in which a flow rate sensing element is disposed, a support member for supporting the sensing passage, and a circuit case, in which an electronic circuit unit for controlling the flow rate sensing element is accommodated, are formed integrally with each other, and the support member extends into a main passage through a hole opened to the main passage so as to position the sensing passage in the main passage. A structural member, the outside shape of which is formed to have a fluid resistance approximately similar to that of the portion of the support member extending from the hole, is disposed at a position approximately symmetrical with the portion of the support member extending from the hole about the sensing passage.

This is a divisional of application Ser. No. 09/456,012 filed Dec. 7,1999, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a flow rate measuring device foroutputting a signal in response to a flow rate, and more specifically toan air flow rate measuring device suitable for measuring, for example,the intake air amount in an internal combustion engine.

2. Description of the Related Art

FIG. 24 and FIG. 25 are a front elevational view and a longitudinalsectional view showing a conventional thermo-sensitive type flow ratesensor disclosed in Japanese Unexamined Patent Publication No. 8-313318,respectively.

In FIG. 24 and FIG. 25, a flow rate sensor 1 comprises a main passage 5through which a fluid to be measured flows, a sensing passage 6 disposedin the main passage 5 substantially coaxially therewith, a flow ratesensing element 12A disposed in the sensing passage 6, a temperaturecompensating resistor 13 disposed in the vicinity of the inlet of thesensing passage 6 in the main passage 5 and an air flow regulating grid7 disposed in the vicinity of the inlet in the main passage 5. Then, acircuit board 8 electrically connected to the flow rate sensing element12A and the temperature compensating resistor 13 is accommodated in acircuit case 9. Further, a connector 10 for supplying power to the flowrate sensor 1 and taking out a flow rate sensing signal to the outsideis disposed on the circuit case 9.

The flow rate sensing element 12A includes a ceramic substrate and aflow rate sensing resistor 11 which is composed of a comb-shapedplatinum film formed on the ceramic substrate. Similarly, thetemperature compensating resistor 13 is composed of a comb-shapedplatinum film formed on the ceramic substrate.

In the conventional flow rate sensor 1 arranged as described above, aheating current flowing to the flow rate sensing resistor 11 of the flowrate sensing element 12A is controlled by a circuit formed in thecircuit board 8 so that the average temperature of the flow rate sensingresistor 11 is made higher than the temperature of the fluid to bemeasured, which is sensed by the temperature compensating resistor 13,by a predetermined temperature. Then, the flow rate of the fluid to bemeasured can be sensed by measuring the heating current supplied to flowrate sensing resistor 11 and converting the heating current into a flowrate signal by making use of the cooling effect of the flow rate sensingresistor 11 cooled by the fluid to be measured and of thecharacteristics that the resistance value of the flow rate sensingresistor 11 is varied by temperature.

FIG. 26 shows the piping of an intake air system when the flow ratesensor 1 is generally used as an intake air flow rate sensor of aninternal combustion engine for automobile. In many cases, the flow ratesensor 1 is disposed downstream of an air cleaner element 2 accommodatedin an air cleaner case 3. The air cleaner element 2 is a filter composedof non-woven fabric, filter paper or the like and is disposed to capturedusts in air drawn by the internal combustion engine and to prevent themfrom entering the interior thereof. Dusts deposit on the air cleanerelement 2 as an automobile travels and it is clogged therewith.Accordingly, differentia of the flow of the intake air having passedthrough the air cleaner element 2 is remarkable as compared with that ofthe flow thereof before the air cleaner element 2 is clogged, and thusthe distribution of flow velocity of the intake air upstream of the flowrate sensor 1 greatly varies.

Since the flow rate sensing element 12A of the flow rate sensor 1obtains flow information by sensing the flow velocity of air in a verysmall portion of the main passage 5, when the distribution of flowvelocity of air upstream of the flow rate sensor 1 varies, an errorarises in a flow rate sensing signal even if the flow velocity does notvary.

Incidentally, as the size of an engine room is reduced recently, thereis an increasing need for the reduction in size of the flow rate sensor.To satisfy this need, proposed is a flow rate sensor of a so-calledplug-in structure which does not include an air flow piping section(main passage 5) as disclosed in, for example, Japanese UnexaminedPatent Publication No. 8-219838. However, since the flow rate sensor ofthe plug-in structure is not provided with the air flow piping section,it is difficult for the flow rate sensor to regulate an air flow usingthe air flow regulator (air flow regulating grid 7) as described above.Therefore, when the flow rate sensor of the plug-in structure is used asan intake air flow rate sensor of an internal combustion engine forautomobile, an error is liable to arise in a flow rate sensing signal atthe time the air cleaner element 2 is clogged.

Further, it is contemplated to mount an air flow regulator on an aircleaner case or an intake air pipe to improve the sensing accuracy ofthe flow rate sensor of the plug-in structure. In this case, the pitchof the air flow regulating elements of the air flow regulator must bemade fine to obtain a sufficient air flow regulating effect. Making thepitch of the air flow regulating elements fine results in an increase ofa pressure loss. Thus, there arises a problem that the amount of airwhich can be drawn by the internal combustion engine is reduced and theoutput thereof is lowered. Further, when the pitch of the air flowregulating elements is too fine, a problem arises in that they areclogged with small dusts having passed through an air cleaner element.In contrast, when the pitch of the air flow regulating elements is madecoarse, not only an air flow regulating effect is lowered but also thethickness of a boundary layer and the frictional stress in a flow ratesensing unit are made uneven by eddies generated downstream and upstreamof the air flow regulator. Accordingly, there arises a problem that aflow cannot be correctly measured because a flow rate sensing signal isdisturbed.

Further, there is a problem that a manufacturing cost is increasedbecause an air regulating structural member is provided in addition tothe flow rate sensor.

A recent thermo-sensing type flow rate sensor employs a flow ratesensing element which is miniaturized to provide a prompt response. Inthis case, when an air flow regulator is disposed upstream of a flowrate sensing element, there is a problem that the flow rate sensingelement is liable to be affected by the fluidic disturbance generated bythe air flow regulator and a flow rate sensing accuracy is deterioratedby the further increase of a noise component included in a flow ratesensing signal.

In addition, the flow rate sensor of the plug-in structure is insertedinto a hole opened to a main passage as shown in, for example, FIG. 1and FiG. 2 of Japanese Unexamined Patent Publication No. 8-219838 andthe sensing passage thereof is located approximately at the center ofthe cross section of the main passage. When the flow rate sensor isviewed from an upstream side, a support member is interposed between thesensing passage and the main passage to support the sensing passage.Accordingly, differentia of a flow resistance is caused in an up/downdirection (the direction in which the support member extends from theinner wall surface of the main passage) about the sensing passage.Further, a flow rate sensor using a plate-shaped air flow regulatingmember disposed below a sensing passage is disclosed in JapaneseUnexamined Patent Publication No. 10-332453. Differentia of a fluidresistance is caused in an upper and lower direction about the sensingpassage also in this case. In the flow rate sensor arranged as describedabove, when a distribution of flow velocity varies upstream of the flowrate sensor, the flow velocity is made uneven in the up/down directionof the flow rate sensor and an error arises in a flow rate sensingsignal.

A flow rate sensor arranged integrally with a fluid temperature sensingelement using a thermistor or the like is disclosed in, for example,Japanese Unexamined Patent Publication No. 8-297040. When the flow ratesensor is viewed from an upstream side, the thermistor is mounted bybeing dislocated in a right or left side about a support member forsupporting a sensing passage. In this case, since differentia of a fluidresistance is caused in the right to left direction about the supportmember, when a distribution of flow velocity varies upstream of the flowrate sensor, an error is liable to arise in a sensed flow.

The flow rate sensor, which uses the thermistor as the fluid temperaturesensing element, is provided with a protector to prevent the damage ofthe thermistor when the flow rate sensor is inserted into an air flowpiping section as disclosed in Japanese Unexamined Patent PublicationNo. 8-297040. However, there is a possibility that the thermistor isdamaged when it is inserted into a hole formed at a sensing passage inthe assembly of the flow rate sensor, and this is not taken intoconsideration.

Further, when a film-shaped flow rate sensing element is used as shownin Japanese Unexamined Patent Publication No. 10-142020, the flow ratesensing element is assembled so that it is substantially in parallelwith the axial direction of a flow rate sensor (the axial direction of asensing passage) as well as the surface thereof is substantially flushwith a plate-shaped member extending into a sensing passage, and an endthereof is buried in a support member and fixed therein. Then, the flowrate sensing element is in electrical conduct to a control circuitsection by a method of wire bonding or the like. Further, the flow ratesensing element is disposed substantially at the center of the crosssection of the sensing passage where a distribution of flow velocity ismade uniform. When it is intended to perform a response from the flowrate sensor at a high speed, the miniaturization of the flow ratesensing element is effective for the purpose. However, the flow ratesensing element is miniaturized, a protective member for protecting theelectric junction at which the flow rate sensing element is electricallyconnected to the control circuit section must be exposed to the sensingpassage to dispose the flow rate sensing element at the center of thesensing passage. In this case, when the sensing passage is viewed froman upstream side, differetia of a flow resistance, which is uneven in anup/down direction, is caused by the protective member. Therefore, whenthe distribution of flow velocity varies upstream of the flow ratesensor, an error arises in a sensed flow.

SUMMARY OF THE INVENTION

An object of the present invention, which was made to solve the aboveproblems, is to obtain a flow rate sensor which can correctly sense aflow even if a distribution of flow velocity varies upstream of the flowrate sensor, has a small pressure loss and is less expensive including amanufacturing cost.

In order to achieve the above object, according to one aspect of thepresent invention, there is provided a flow rate sensor comprising aflow rate sensing element for sensing the flow rate of a fluid, asensing passage into which the fluid is introduced and in which the flowrate sensing element is disposed, a support member for supporting thesensing passage and a circuit case in which an electronic circuit unitfor controlling the flow rate sensing element is accommodated, whereinthe sensing passage, the support member and the circuit case are formedintegrally with each other and the support member extends into a mainpassage, through which the fluid flows, through a hole opened to themain passage so as to position the sensing passage in the main passage.The flow rate sensor further comprises a structural member whose theoutside shape is formed to have a fluid resistance approximately similarto that of the portion of the support member extending from the hole,wherein the structural member is disposed at a position approximatelysymmetrical with the portion of the support member extending from thehole about the sensing passage.

According to another aspect of the present invention, there is provideda flow rate sensor comprising a flow rate sensing element for sensingthe flow rate of a fluid, a sensing passage into which the fluid isintroduced and in which the flow rate sensing element is disposed, asupport member for supporting the sensing passage, a circuit case inwhich an electronic circuit unit for controlling the flow rate sensingelement is accommodated and a fluid temperature sensing element forsensing the temperature of the fluid, wherein the sensing passage, thesupport member and the circuit case is formed integrally with each otherand the support member extends into a main passage, through which thefluid flows, through a hole opened to the main passage so as to positionthe sensing passage and the fluid temperature sensing element in themain passage. The flow rate sensor further comprises a protector forprotecting the fluid temperature sensing element, and a structuralmember whose the outside shape is formed to have a fluid resistanceapproximately similar to that of the protector, wherein the protectorand the structural member are disposed at positions approximatelysymmetrical with respect to the support member for supporting thesensing passage.

According to still another aspect of the present invention, there isprovided a flow rate sensor comprising a flow rate sensing element forsensing the flow rate of a fluid, a sensing passage into which the fluidis introduced and in which the flow rate sensing element is disposed, asupport member for supporting the sensing passage, a sensing assistantmember disposed so as to extend into the sensing passage for supportingthe flow rate sensing element and a circuit case in which an electroniccircuit unit for controlling the flow rate sensing element isaccommodated. The flow rate sensor further comprises a protective memberdisposed so as to project into the sensing passage for protecting anelectric junction, at which the electronic circuit unit is connected tothe flow rate sensing element, from the fluid in cooperation with thesensing assistant member, and a structural member the outside shape ofwhich is formed to have a fluid resistance approximately similar to thatof the portion of the protective member projecting into the sensingpassage, the structural member being located at a position approximatelysymmetrical with the portion of the protective member projecting intothe sensing passage about the axial center of the sensing passage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 1 of the present invention;

FIG. 2 is a longitudinal sectional view showing the flow rate sensoraccording to the embodiment 1 of the present invention;

FIG. 3 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 2 of the present invention;

FIG. 4 is a longitudinal sectional view showing the flow rate sensoraccording to the embodiment 2 of the present invention;

FIG. 5 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 3 of the present invention;

FIG. 6 is a longitudinal sectional view showing the flow rate sensoraccording to the embodiment 3 of the present invention;

FIG. 7 is a partial lateral sectional view showing another embodiment ofthe flow rate sensor according to the embodiment 3 of the presentinvention;

FIG. 8 is a longitudinal sectional view showing the another embodimentof the flow rate sensor according to the embodiment 3 of the presentinvention;

FIG. 9 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 4 of the present invention;

FIG. 10 is a partial longitudinal sectional view showing the flow ratesensor according to the embodiment 4 of the present invention;

FIG. 11 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 5 of the present invention;

FIG. 12 is a longitudinal sectional view showing the flow rate sensoraccording to the embodiment 5 of the present invention;

FIG. 13 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 6 of the present invention;

FIG. 14 is a longitudinal sectional view showing the flow rate sensoraccording to the embodiment 6 of the present invention;

FIG. 15 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 7 of the present invention;

FIG. 16 is a partial longitudinal sectional view showing the flow ratesensor according to the embodiment 7 of the present invention;

FIG. 17 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 8 of the present invention;

FIG. 18 is a partial longitudinal sectional view showing the flow ratesensor according to the embodiment 8 of the present invention;

FIG. 19 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 9 of the present invention;

FIG. 20 is a partial longitudinal sectional view showing the flow ratesensor according to the embodiment 9 of the present invention;

FIG. 21 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 10 of the present invention;

FIG. 22 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 11 of the present invention;

FIG. 23 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 12 of the present invention;

FIG. 24 is a front elevational view showing a conventional flow ratesensor;

FIG. 25 is a longitudinal sectional view showing the conventional flowrate sensor; and

FIG. 26 is a view of the piping of an intake air system of an internalcombustion engine for automobile to which the conventional flow ratesensor is applied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below.

Embodiment 1

FIG. 1 and FIG. 2 are a partial lateral sectional view and alongitudinal sectional view showing a flow rate sensor according to anembodiment 1 of the present invention, respectively.

In FIG. 1 and FIG. 2, a main passage 16 is a cylindrical tube made of aresin through which a fluid to be measured flows. The main passage 16 isformed integrally with, for example, an air cleaner case disposed to thepiping of the intake air system of an internal combustion engine forautomobile. A flow rate sensor 100 is formed as a so-called plug-instructure which is mounted to the main passage 16 so as to sense theflow rate of a fluid flowing therein. The flow rate sensor 100 comprisesa support member 20, a cylindrical sensing passage 19, a plate-shapedsensing assistant member 22, a flow rate sensing element 12, astructural member 21 and a circuit case 15. The sensing passage 19 isdisposed at an end of the support member 20 so that the axial centerdirection thereof is perpendicular to the lengthwise direction of thesupport member 20; the sensing assistant member 22 extends from theinner wall surface of the sensing passage 19 in the lengthwise directionof the support member 20 so that the main surface thereof passes throughthe axial center of the sensing passage 19; the flow rate sensingelement 12 is assembled to the sensing assistant member 22 so that thesurface thereof is flush with the sensing assistant member 22 with anend thereof fixed in the support member 20; the structural member 21extends from the outer wall surface of the sensing passage 19 in thelengthwise direction of the support member 20 so as to be located at aposition symmetrical with the support member 20 with respect to thesensing passage 19; and the circuit case 15 is disposed to the other endof the support member 20. The sensing passage 19, the support member 20and the circuit case 15 are molded of a resin integrally with eachother. That is, they are formed as an integral resin body.

The flow rate sensor 100 is inserted into the main passage 16 through anopening 30 formed thereat so that the support member 20 extends from theinner wall surface of the main passage 16 thereinto. Then, the flow ratesensor 100 is mounted on the main passage 16 by tightening and fixingthe circuit case 15 to the outer wall thereof by screws (not shown). Atthe time, an O-ring 29 is interposed between the support member 20 andthe opening 30 of the main passage 16, thereby securing the airtightness of the main passage 16. The sensing passage 19 is disposed inthe main passage 16 approximately coaxially therewith. Further, theaxial center direction of the sensing passage 19 is approximately inagreement with the flow direction 4 of the fluid to be measured.Further, the structural member 21 is formed to a shape similar to thatof a portion of the section, which projects into the main passage 16, ofthe support member 20.

A circuit board 14 as an electronic circuit unit is accommodated in thecircuit case 15 to control an electric signal. Then, terminals 23connected to the circuit board 14 are electrically connected to the flowrate sensing element 12 through leads 24 in the support member 20.Further, a connector 18 is disposed to the circuit case 15 so that powercan be supplied from the outside to the flow rate sensor 100 and a flowsignal sensed by the flow rate sensor 100 can be taken out to theoutside.

The flow rate sensing element 12 is composed of a comb-shaped flow ratesensing resistor 11 and a temperature compensating resistor 13 formed ona silicon substrate compositely by patterning a platinum film depositedon the silicon substrate. A heat insulating means (not shown) isdisposed to prevent the heat conduction from the flow rate sensingresistor 11 to the temperature compensating resistor 13.

In the following description, the lengthwise direction of the supportmember 20, that is, the direction in which the support member 20 extendsfrom the inner wall surface of the main passage 16 is defined as anup/down direction, and the direction perpendicular to the axial centerof the sensing passage 19 and to the lengthwise direction of the supportmember 20 is defined as a right to left direction. This definition isalso applied to the embodiments which will be described hereafter. Toobtain the effect of the present invention, the temperature compensatingresistor 13 is not necessarily formed on the flow rate sensing element12 and only the flow rate sensing resistor 11 may be formed to the flowrate sensing element 12. Further, the substrate of the flow rate sensingelement 12 is not limited to the silicon substrate and any substrate maybe used so long as it is an electric insulator, and the substrate maybe, for example, a ceramic substrate. Further, the material of the flowrate sensing resistor 11 and the temperature compensating resistor 13 isnot limited to platinum and may be any material so long as it is athermo-sensitive resistance material, and it may be, for example,nickel, permalloy and the like.

In the flow rate sensor 100 arranged as described above, since thestructural member 21 is formed to the shape similar to that of a portionof the section, which projects into the main passage 16, of the supportmember 20, a portion of the support member 20 in the main passage 16 andthe structural member 21 have the same fluid resistance. Further, sincethe structural member 21 and the support member 20 are disposedsymmetrically about the sensing passage 19, the fluid resistance is madeuniform in the up/down direction.

Thus, even if differentia of the distribution of flow velocity of thefluid to be measured, which flows into the main passage 16, is caused,the component of flow velocity in a main flow axis direction iscorrected at least in the up/down direction and the distribution of flowvelocity of the fluid to be measured is averaged in the main flow axisdirection. As a result, an error is difficult to arise in a sensed flowand a flow rate can be correctly sensed.

Note that while the structural member 21 is formed to the shape similarto that of a portion of the section, which projects into the mainpassage 16, of the support member 20 in the embodiment 1, it is notnecessarily formed to the similar shape and it is sufficient for them tohave substantially the same flow resistance.

Further, a distance L is put between the structural member 21 and theinner wall surface of the main passage 16 in the embodiment 1, and it ispreferable that distance L is set to one half or less the inside radiusr of the main passage 16 because a fluid resistance is made by thefriction stress of the wall surface in the vicinity of the inner wallsurface of the main passage 16.

Embodiment 2

FIG. 3 and FIG. 4 are a partial lateral sectional view and alongitudinal sectional view showing a flow rate sensor according to anembodiment 2 of the present invention, respectively.

As shown in FIG. 3 and FIG. 4, in the embodiment 2, a structural member21A is disposed in a sensing passage 19 at a position approximatelysymmetrical with a support member 20 about the sensing passage 19. Thestructural member 21A is molded of, for example, a resin or the likeintegrally with the sensing passage 19 and has a fluid resistancesubstantially approximately similar to that of the portion of a supportmember 20 projecting into a main passage 16. Further, the structuralmember 21A is formed by extracting a predetermined solid portion fromthe interior thereof.

Note that the other arrangement of the embodiment 2 is similar to thatof the embodiment 1.

In the flow rate sensor 101 arranged as described above, since theamount of the resin necessary to form the structural member 21A can bereduced, the flow rate sensor of light weight can be obtained at a lessexpensive cost, in addition to the effect of the embodiment 1.

Further, since the moment of the sensing passage 19 including thestructural member 21A is reduced, the strength of the support member 20of the sensing passage 19 can be lowered and thus the width of thesupport member 20 can be narrowed, whereby a pressure loss can bereduced.

Embodiment 3

FIG. 5 and FIG. 6 are a partial lateral sectional view and alongitudinal sectional view showing a flow rate sensor according to anembodiment 3 of the present invention, respectively.

As shown in FIG. 5 and FIG. 6, in the embodiment 3, a mounting section19 a is disposed to the outer peripheral wall of a sensing passage 19 ina projecting state at a position symmetrical with a support member 20,and further a structural member 21B is fixed to the mounting section 19a by soldering. Then, the portion composed of the mounting section 19 aand the structural member 21B and projecting from the sensing passage 19is formed to an outside shape whose flow resistance is substantiallyapproximately similar to that of the portion of the support member 20projecting into a main passage 16. Further, the structural member 21Band the support member 20 have a symmetrical positional relationshipabout the sensing passage 19.

Note that the other arrangement of the embodiment 3 is similar to thatof the embodiment 1.

When this type of the flow rate sensor is standardized as an intake airflow rate sensor for an internal combustion engine for automobile havingseveral kinds of displacement amounts and applied thereto, the mainpassage 16 to which the flow rate sensor is mounted has several kinds ofinside diameters in accordance with the displacements and outputs of theinternal combustion engine.

In the flow rate sensor 102 arranged as described above, the sensingpassage 19 and the structural member 21B are formed as separate members.Thus, when several kinds of the structural members 21B having variouslengths in a diametrical direction are prepared, a structural member 21Bhaving a suitable length can be selected and combined in accordance withthe inside diameter of a main passage 16 to which it is applied. As aresult, the structural components of the flow rate sensor 102 other thanthe structural member 21B can be standardized. According to theembodiment 3, the flow rate sensor of low cost can be obtained, inaddition to the effect of the embodiment 1.

Note that while the structural member 21B is soldered to the mountingsection 19 a of the sensing passage 19 in the embodiment 3, a method offixing the sensing passage 19 to the structural member 21B is notlimited to the soldering, and the structural member 21B may be fixed tothe mounting section 19 a by bonding or through screws.

In the embodiment 3, while the structural member 21B is fixed to themounting section 19 a disposed to the sensing passage 19, the structuralmember 21B may be directly fixed to the sensing passage 19.

Further, while the sensing passage 19 is formed to a cylindrical shapein the embodiment 3, the shape thereof is not limited to the cylindricalshape and may be formed to, for example, a rectangular shape as shown inFIG. 7 and FIG. 8 and further may be formed to an elliptic cylindricalshape.

Embodiment 4

FIG. 9 and FIG. 10 are a partial lateral sectional view and alongitudinal sectional view showing a flow rate sensor according to anembodiment 4 of the present invention, respectively.

As shown in FIG. 9 and FIG. 10, in the embodiment 4, a thermistor 25 asa fluid temperature sensing element is disposed to a circuit case 15 soas to be exposed in a main passage 16. A protector 26 is disposed to asupport member 20 to protect the thermistor 25. Further, a structuralmember 21C having a shape similar to that of the protector 26 isdisposed at a position approximately symmetrical with the protector 26about the support member 20 of a sensing passage 19.

Note that the other arrangement of the embodiment 4 is similar to thatof the embodiment 1.

In the flow rate sensor 103 arranged as described above, since theprotector 26 and the structural member 21C have approximately the samefluid resistance as well as they are disposed symmetrically about thesensing passage 19, a fluid resistance is made uniform on the right andleft sides of the sensing passage 19.

Thus, even if differentia of the distribution of flow velocity of thefluid to be measured, which flows into the main passage 16, is caused,the component of flow velocity in a main flow axis direction iscorrected at least in a right to left direction and the distribution offlow velocity of the fluid to be measured is averaged in the main flowaxis direction because the fluid resistance is made uniform on the rightand left sides of the sensing passage 19. Therefore, an error isdifficult to arise in a sensed flow and a flow rate can be correctlysensed.

Embodiment 5

FIG. 11 and FIG. 12 are a partial lateral sectional view and alongitudinal sectional view showing a flow rate sensor according to anembodiment 5 of the present invention, respectively.

In FIG. 11 and FIG. 12, the flow rate sensor 104 comprises a cylindricalmain passage 16A which is made of a resin and through which a fluid tobe measured flows, a cylindrical sensing passage 19, a support member20, a plate-shaped sensing assistant member 22, a flow rate sensingelement 12 and a circuit case 15. The sensing passage 19 is disposed inthe main passage 16A approximately coaxially therewith; the supportmember 20 extends from the inner wall surface of the main passage 16Aand supports the sensing passage 19; the sensing assistant member 22extends from the inner wall surface of the sensing passage 19 in thedirection in which the support member 20 extends so that the mainsurface thereof passes through the axial center of the sensing passage19; the flow rate sensing element 12 is assembled to the sensingassistant member 22 so that the surface thereof is flush with thesensing assistant member 22 with an end thereof fixed in the supportmember 20; and the circuit case 15 is disposed to the outer wall surfaceof the main passage 16A.

Terminals 23 are electrically connected to the flow rate sensing element12 through leads 24 in the support member 20. A flow rate sensingresistor 11 formed to the miniaturized flow rate sensing element 12 isdisposed so as to be located approximately at the center of the sensingpassage 19. Further, the electric junctions where the terminals 23 areconnected to the leads 24 and the leads 24 are connected to the flowrate sensing resistor 11 are protected from the fluid to be measured bya protective member 27 which is formed integrally with the sensingassistant member 22. The protective member 27 is disposed such that aportion thereof is exposed in the sensing passage 19. Further, astructural member 21D, which has a shape approximately similar to thatof the portion of the protective member 27 exposed in the sensingpassage 19, is disposed on the inner wall surface of the sensing passage19 at a position approximately symmetrical with the exposed portion ofthe protective member 27 about the axial center of the sensing passage19.

Note that the protective member 27 need not be formed integrally withthe sensing assistant member 22 to obtain the effect of the presentinvention and it may be formed separately therefrom. This is alsoapplicable to the embodiments described below.

Miniaturization of the flow rate sensing element 12 is effective toobtain a high speed response from the flow rate sensor. However, whenthe miniaturization of the flow rate sensing element 12 is promoted, theprotective member 27 for protecting the lead 24 must be exposed in thesensing passage 19 in order to dispose the flow rate sensing resistor11, which is formed on the flow rate sensing element 12, approximatelyat the center of the sensing passage 19 in which a distribution of flowvelocity is made uniform. Otherwise, a flow resistance is made uneven inthe up/down direction in the sensing passage 19. Thus, when thedistribution of flow velocity varies upstream of the flow rate sensor,an error is liable to be arisen in a sensed flow.

According to the embodiment 5, the structural member 21D having theshape, which is approximately similar to that of the portion of theprotective member 27 exposed in the sensing passage 19, is disposed onthe inner wall surface of the sensing passage 19 at the positionapproximately symmetrical with the exposed portion of the protectivemember 27 about the axial center of the sensing passage 19. Accordingly,the fluid resistance is made uniform in the up/down direction of thesensing assistant member 22 of the flow rate sensing element 12. As aresult, even if the distribution of flow velocity varies upstream of theflow rate sensor 104, an error is difficult to be arisen in a sensedflow and a flow rate can be correctly sensed because the component offlow velocity in the main flow axis direction is corrected at least inthe up/down direction in the sensing passage 19 and the distribution offlow velocity of the fluid to be measured is averaged in the main flowaxis direction.

Embodiment 6

FIG. 13 and FIG. 14 are a partial lateral sectional view and alongitudinal sectional view showing a flow rate sensor according to anembodiment 6 of the present invention, respectively.

As shown in FIG. 13 and FIG. 14, in the embodiment 6, a structuralmember 21E, which has a fluid resistance approximately similar to thatof the portion of a protective member 27 exposed in a sensing passage19, is made of, for example, a resin or the like and formed integrallywith a sensing assistant member 22 which is also made of the resin orthe like. The structural member 21E is disposed at a positionapproximately symmetrical with the exposed portion of the protectivemember 27 about the axial center of the sensing passage 19.

Note that the other arrangement of the embodiment 6 is similar to thatof the embodiment 5.

In the flow rate sensor 105 arranged as described above, since thestructural member 21E, which has the fluid resistance approximatelysimilar to that of the portion of the protective member 27 exposed inthe sensing passage 19, is made of, for example, the resin or the likeand formed integrally with the sensing assistant member 22 which is alsomade of the resin or the like, it has the following effect, in additionto the effect of the embodiment 5. That is, when the sensing assistantmember 22 is assembled to the structural member 21E, their assembledpositions are not relatively dislocated as compared with the case thatthe structural member 21D is formed separately from the sensingassistant member 22 as shown in the embodiment 5 because the positionswhere they are assembled are not dispersed. Accordingly, the dispersionof the flow characteristics of the flow rate sensor can be reduced.

Embodiment 7

FIG. 15 and FIG. 16 are a partial lateral sectional view and alongitudinal sectional view showing a flow rate sensor according to anembodiment 7 of the present invention, respectively.

As shown in FIG. 15 and FIG. 16, in the embodiment 7, a thermistor 25 asa fluid temperature sensing element and a protector 26 are formed as anintegral unit. The unit is inserted into a main passage 16 through ahole 31 formed at a circuit case 15 so that the thermistor 25 is exposedtherein.

Note that the other arrangement of the embodiment 7 is similar to thatof the embodiment 1.

In the flow rate sensor 106 arranged as described above, since thethermistor 25 and the protector 26 are made of, for example, a resin orthe like and previously formed integrally with each other, thethermistor 25 does not come into contact or collide with a main passage16 when the flow rate sensor 106 is assembled to the hole 30 formed tothe main passage 16. Further, when the thermistor 25 is inserted intothe hole 31 formed at the circuit case 15 in the manufacture of flowrate sensor 106, the thermistor 25 does not come into contact or collidewith the circuit case 15. As a result, the yield of the flow rate sensorcan be improved in the manufacture thereof and the manufacturing costthereof can be reduced.

Embodiment 8

FIG. 17 and FIG. 18 are a partial lateral sectional view and alongitudinal sectional view showing a flow rate sensor according to anembodiment 8 of the present invention, respectively.

As shown in FIG. 17 and FIG. 18, in the embodiment 8, a thermistor 25 asa fluid temperature sensing element and a protector 26 are formed as anintegral unit. Then, the protector 26 is formed so as to leave thethermistor 25 to view from the upstream side and the downstream side.The unit is inserted into a main passage 16 through a hole 31 formed ata circuit case 15 so that the thermistor 25 is exposed therein.

Note that the other arrangement of the embodiment 8 is similar to thatof the embodiment 7.

In the flow rate sensor 107 arranged as described above, since nostructural member is disposed upstream of the thermistor 25, thethermistor 25 can be easily in contact with a fluid to be measured andthus the temperature of the fluid can be correctly measured, in additionto the effect of the embodiment 7.

Embodiment 9

FIG. 19 and FIG. 20 are a partial lateral sectional view and alongitudinal sectional view showing a flow rate sensor according to anembodiment 9 of the present invention, respectively.

As shown in FIG. 19 and FIG. 20, in the embodiment 9, a thermistor 25 asa fluid temperature sensing element and a protector 26 are formed as anintegral unit. The unit is inserted into a main passage 16 through ahole 31 formed at a circuit case 15 so that the thermistor 25 is exposedtherein. Further, a projecting structural body 28 is formed to thesupport member 20 of a sensing passage 19 integrally therewith so as tobe in contact with the protector 26.

Note that the other arrangement of the embodiment 9 is similar to thatof the embodiment 7.

In the flow rate sensor 108 arranged as described above, when thethermistor 25, which is formed integrally with the protector 26, isinserted into the main passage 16 through the hole 31 formed at thecircuit case 15 and assembled by being spaced apart from the supportmember 20 of the sensing passage 19 in the manufacture of the flow ratesensor, it is positioned at the two points, that is, at the hole 31formed at the circuit case 15 and at the structural member 28 and fixedthereat. Accordingly, a flow rate sensor having reliability in strengthcan be obtained, in addition to the effect of the embodiment 7 becausethe protector 26 and the thermistor 25 are neither broken nor destroyedby external force when the flow rate sensor is assembled to the mainpassage 16.

Further, positional dislocation is difficult to be arisen in theassembly of the thermistor 25, and thus the dispersion of the flowcharacteristics of the flow rate sensor due to the dispersion of theassembled positions of the thermistor 25 can be reduced.

Embodiment 10

FIG. 21 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 10 of the present invention.

As shown in FIG. 21, in the embodiment 10, a structural member 21Fhaving a shape similar to that of the protector 26 is disposed at aposition approximately symmetrical with the protector 26 about thesupport member 20 of a sensing passage 19.

Note that the other arrangement of the embodiment 10 is similar to thatof the embodiment 7.

In the flow rate sensor 109 arranged as described above, since theprotector 26 and the structural member 21F have approximately the samefluid resistance as well as they are disposed symmetrically about thesensing passage 19, it has the following effect, in addition to theeffect of the embodiment 7. That is, a fluid resistance is made uniformon the right and left sides of the sensing passage 19. Thus, even ifdifferentia of the distribution of flow velocity of the fluid to bemeasured, which flows into the main passage 16, is caused, the componentof flow velocity in a main flow axis direction is corrected at least ina right to left direction and the distribution of flow velocity of thefluid to be measured is averaged in the main flow axis direction becausethe fluid resistance is made uniform on the right and left sides of thesensing passage 19. Therefore, an error is difficult to arise in asensed flow and a flow rate can be correctly sensed.

Embodiment 11

FIG. 22 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 10 of the present invention.

As shown in FIG. 22, in the embodiment 11, a structural member 21Ghaving a shape similar to that of the protector 26 is disposed at aposition approximately symmetrical with the protector 26 about thesupport member 20 of a sensing passage 19.

Note that the other arrangement of the embodiment 11 is similar to thatof the embodiment 8.

In the flow rate sensor 110 arranged as described above, since theprotector 26 and the structural member 21G have approximately the samefluid resistance as well as they are disposed symmetrically about thesensing passage 19, it has the following effect, in addition to theeffect of the embodiment 8. That is, a fluid resistance is made uniformon the right and left sides of the sensing passage 19. Thus, even ifdifferentia of the distribution of flow velocity of the fluid to bemeasured, which flows into the main passage 16, is caused, the componentof flow velocity in a main flow axis direction is corrected at least ina right to left direction and the distribution of flow velocity of thefluid to be measured is averaged in the main flow axis direction becausethe fluid resistance is made uniform on the right and left sides of thesensing passage 19. Therefore, an error is difficult to arise in asensed flow and a flow rate can be correctly sensed.

Embodiment 12

FIG. 23 is a partial lateral sectional view showing a flow rate sensoraccording to an embodiment 10 of the present invention.

As shown in FIG. 23, in the embodiment 12, a structural member 21Hhaving a shape similar to that of the protector 26 and the structuralbody 28 is disposed at a position approximately symmetrical with theprotector 26 and the structural body 28 about the support member 20 of asensing passage 19.

Note that the other arrangement of the embodiment 12 is similar to thatof the embodiment 9.

In the flow rate sensor 111 arranged as described above, since thestructural member 21H and, the protector 26 and the structural body 28have approximately the same fluid resistance as well as they aredisposed symmetrically about the sensing passage 19, it has thefollowing effect, in addition to the effect of the embodiment 9. Thatis, a fluid resistance is made uniform on the right and left sides ofthe sensing passage 19. Thus, even if differentia of the distribution offlow velocity of the fluid to be measured, which flows into the mainpassage 16, is caused, the component of flow velocity in a main flowaxis direction is corrected at least in a right to left direction andthe distribution of flow velocity of the fluid to be measured isaveraged in the main flow axis direction because the fluid resistance ismade uniform on the right and left sides of the sensing passage 19.Therefore, an error is difficult to arise in a sensed flow and a flowrate can be correctly sensed.

Since the present invention is arranged as described above, it canachieve the following effects.

According to the present invention, in the flow rate sensor comprisingthe flow rate sensing element for sensing the flow rate of a fluid, asensing passage into which the fluid is introduced and in which the flowrate sensing element is disposed, the support member for supporting thesensing passage and the circuit case in which the electronic circuitunit for controlling the flow rate sensing element is accommodated,wherein the sensing passage, the support member and the circuit case areformed integrally with each other and the support member extends intothe main passage, through which the fluid flows, through the hole openedto the main passage so as to position the sensing passage in the mainpassage, the flow rate sensor further comprises the structural memberwhose the outside shape is formed to have a fluid resistanceapproximately similar to that of the portion of the support memberextending from the hole, wherein the structural member is disposed atthe position approximately symmetrical with the portion of the supportmember extending from the hole about the sensing passage. Accordingly,there can be obtained the flow rate sensor capable of sensing the flowrate of the fluid to be measured at a pinpoint accuracy even if thedistribution of flow velocity of the fluid varies.

Since the structural member is formed by extracting the predeterminedsolid portion from the interior thereof, the cost and weight of the flowrate sensor can be reduced.

Since at least a portion of the structural member is formed as acomponent separated from the sensing passage and fixed to the sensingpassage or to the mounting section disposed in the sensing passage bythe fixing means, the flow rate sensor is suitable as an intake air flowrate sensor of an internal combustion engine for automobile having adifferent displacement.

In the flow rate sensor comprising the flow rate sensing element forsensing the flow rate of a fluid, the sensing passage into which thefluid is introduced and in which the flow rate sensing element isdisposed, the support member for supporting the sensing passage, thecircuit case in which the electronic circuit unit for controlling theflow rate sensing element is accommodated and the fluid temperaturesensing element for sensing the temperature of the fluid, wherein thesensing passage, the support member and the circuit case is formedintegrally with each other and the support member extends into the mainpassage, through which the fluid flows, through the hole opened to themain passage so as to position the sensing passage and the fluidtemperature sensing element in the main passage, the flow rate sensorfurther comprises the protector for protecting the fluid temperaturesensing element, and the structural member whose the outside shape isformed to have a fluid resistance approximately similar to that of theprotector, wherein the protector and the structural member are disposedat the positions approximately symmetrical with respect to the supportmember for supporting the sensing passage. Accordingly, there can beobtained the flow rate sensor capable of sensing the flow rate of thefluid to be measured at a pinpoint accuracy even if the distribution offlow velocity of the fluid vanes.

Since the fluid temperature sensing element is formed integrally withthe sensing passage, the support member and the circuit case, positionaldislocation is difficult to be arisen in the assembly of the fluidtemperature sensing element.

Since the fluid temperature sensing element and the protector are formedintegrally with each other as a unit and a hole, into which the unit isinserted, is opened to the support member or to the circuit case, therecan be obtained the flow rate sensor whose yield can be improved andwhose manufacturing cost can be reduced.

Further, since a structural body for supporting the unit is formedintegrally with the support member, positional dispersion can be reducedwhen parts are assembled, whereby the dispersion of flow characteristicscan be decreased.

In the flow rate sensor comprising a flow rate sensing element forsensing the flow rate of a fluid, the sensing passage into which thefluid is introduced and in which the flow rate sensing element isdisposed, the support member for supporting the sensing passage, thesensing assistant member disposed so as to extend into the sensingpassage for supporting the flow rate sensing element and the circuitcase in which the electronic circuit unit for controlling the flow ratesensing element is accommodated, the flow rate sensor further comprisesthe protective member disposed so as to project into the sensing passagefor protecting the electric junction, at which the electronic circuitunit is connected to the flow rate sensing element, from the fluid incooperation with the sensing assistant member, and the structural memberwhose the outside shape is formed to have a fluid resistanceapproximately similar to that of the portion of the protective memberprojecting into the sensing passage, the structural member being locatedat the position approximately symmetrical with the portion of theprotective member projecting into the sensing passage about the axialcenter of the sensing passage. Accordingly, there can be obtained theflow rate sensor capable of sensing the flow rate of the fluid to bemeasured at a pinpoint accuracy even if the distribution of flowvelocity of the fluid varies.

Since the structural member is formed integrally with the sensingassistant member, the dispersion of the flow characteristics of the flowrate sensor can be reduced.

In the flow rate sensor comprising the flow rate sensing element forsensing the flow rate of a fluid, the sensing passage into which thefluid is introduced and in which the flow rate sensing element isdisposed, the support member for supporting the sensing passage, thecircuit case in which the electronic circuit unit for controlling theflow rate sensing element is accommodated, the fluid temperature sensingelement for sensing the temperature of the fluid and the protector forprotecting the fluid temperature sensing element, the sensing passage,the support member and the circuit case being formed integrally witheach other and the support member extending into the main passage,through which the fluid flows, through the hole opened to the mainpassage so as to position the sensing passage in the main passage,wherein the fluid temperature sensing element and the protector areformed integrally with each other as the unit and the hole, into whichthe unit is inserted, is opened to the support member or to the circuitcase. Accordingly, there can be obtained the flow rate sensor whoseyield can be improved and whose manufacturing cost can be reduced.

Further, since the structural member for supporting the unit is formedintegrally with the support member, positional dispersion can be reducedwhen parts are assembled, whereby the dispersion of flow characteristicscan be decreased.

What is claimed is:
 1. A flow rate sensor comprising a flow rate sensingelement for sensing the flow rate of a fluid, a sensing passage intowhich the fluid is introduced and in which the flow rate sensing elementis disposed, a support member for supporting the sensing passage and acircuit case in which an electronic circuit unit for controlling theflow rate sensing element is accommodated, wherein the sensing passage,the support member and the circuit case are formed integrally with eachother and the support member extends into a main passage, through whichthe fluid flows, through a hole opened to the main passage so as toposition the sensing passage in the main passage, the flow rate sensorcomprising: a structural member having an outside shape is formed tohave a fluid resistance approximately similar to that of the portion ofthe support member extending from the hole, wherein said structuralmember is disposed at a position approximately symmetrical with theportion of the support member extending from the hole about the sensingpassage.
 2. A flow rate sensor according to claim 1, wherein apredetermined solid portion is being removed from an interior of saidstructural member.
 3. A flow rate sensor according to claim 1, whereinat least a portion of said structural member is formed as a componentseparated from the sensing passage and fixed to the sensing passage orto a mounting section disposed in the sensing passage by a fixing means.